Thermal Transformation of Cis-((Mo(Co)(3)H)(2)(Mu-Eta(5)Eta(5)-C5H3(Sime(2))(2)C5H3)) and Trans-((Mo(Co)(3)H)(2)(Mu-Eta(5)Eta(5)-C5H3(Sime(2))(2)C5H3)) into ((Mo(Co)(3))(2)(Mu-Eta(5)Eta(5)-C5H4(Sime(2)Sime(2))-C5H4))(Mo-Mo) Promoted by Hydride Migration